Ok, the fuel line still bothers me. The replacement I recently got wasnt totally satisfactory, as I noticed the R-thread adapter cone on the replacement had a hole with smaller diameter.
Below, I have a picture of the stock one. This is not from my MR2, instead I bought a used one to examine it and get it right.
To make clear what bit I have here, this is the rubber line that comes between the fuel tank hard line and the fuel filter.
Fuel filter end has a banjo with 5mm diameter hole. Banjo and the bolt itself are 12mm (M12 x 1.25 to be exact)
This end of the line seems to have a shallow cone or a ball head, I just cant make it out which one it is, but it is supposed to seal against the fuel tank hard line that has a similarly sized flare and a flare nut behind it.
The threads don’t seal the connection, but the nuts should be tightened well to make sure the flare is well pressed against the cone to make the actual seal.
This very phallic looking thing is a cheap hose barb which has the exact same thread as the fuel line. I can now confirm, that the thread on the fuel line is 1/4″ R-thread, also known as British Standard Pipe Parallel (BSPP) and it has a 19 threads per inch (TPI) – 1/4″ -19 BSP(P)
It is exceptionally hard to find an adapter for it that has bigger diameter hole to fuel to pass through! Even harder if you want to have something like AN/JIC -terminal on the other side 😀